WO2018185500A1

WO2018185500A1 - Apparatus and methods for aqueous organic waste treatment

Info

Publication number: WO2018185500A1
Application number: PCT/GB2018/050936
Authority: WO
Inventors: Nigel Willis Brown; Mikael KHAN
Original assignee: Arvia Technology Limited
Priority date: 2017-04-07
Filing date: 2018-04-09
Publication date: 2018-10-11
Also published as: CN110730763A; GB201705646D0; EP3606877A1

Abstract

An apparatus for the treatment of an aqueous organic waste liquid to provide a treated liquid containing less organic matter, the apparatus comprising: a treatment reservoir defining first and second zones separated by a porous separator, carbon-based adsorbent material capable of electrochemical regeneration provided in said first and second zones, the adsorbent material in each zone being coupled to a source of electrical power for providing a potential difference between the adsorbent material in each zone such that the adsorbent material in a first zone acts as an anode and the adsorbent material in a second zone acts as a cathode; wherein the total surface area of the adsorbent material in the first zone is different to the total surface area of the adsorbent material in the second zone. A method for the treatment of an aqueous organic waste liquid is also described.

Description

APPARATUS AND METHODS FOR

AQUEOUS ORGANIC WASTE TREATMENT

The present invention relates to methods and apparatus for the treatment of aqueous organic wastes, particularly but not exclusively aqueous wastes containing organic components and bulk organic wastes that have been dispersed, emulsified or dissolved in water.

Many methods have been developed to treat aqueous organic wastes. Prior art methods typically exploit the treatment of aqueous organic wastes through the contacting of the waste with a porous material. Porous materials contain internal pores, into which organic components are either adsorbed or absorbed, depending upon the nature of dissolution of the organic component in the water. Irrespective of the take-up mechanism, the presence of internal pores has negative implications for the regeneration of porous materials. Prior research into this area seeks to increase the absorptive capacity of absorbent materials at the expense of complex and difficult regeneration.

Regeneration refers to the removal of contaminants from a material for subsequent re-use. Regeneration can be achieved in a number of ways, including electrochemically, thermally, biologically, and chemically. Electrochemical regeneration refers to the passage of an electrical current through the material to effect destruction of the adsorbed contaminants via oxidative electrochemical processes. However, as established in "Electrochemical regeneration of granular activated carbon"; R M Narbaitz, J Cen; Wat. Res. 28 (1994) 1771 - 1778, it is advantageous to cathodically desorb pollutants and then oxidise the desorbed pollutants at the anode. As such, the treatment involves desorption followed by oxidation. Organic components adsorbed or absorbed into the internal pores of the material are not oxidised when exposed to an electric current. Instead, the notoriously expensive regeneration of the porous materials is usually achieved by high energy, thermal exposure over long time scales. Alternatively, the loaded porous material may be disposed of, e.g. to landfill, instead of utilising expensive regeneration processes to enable re-use.

The system and method described in UK patent no. GB2470042B obviates or mitigates many of the problems previously associated with the removal of organic components from aqueous waste. The invention described in this patent relates to the treatment of aqueous organic wastes by the adsorption of the organic components followed by subsequent oxidation of the organic components and simultaneous regeneration of the adsorbent, within a single unit, using relatively low power and circumventing the need to dispose of, or thermally regenerate, the material used during treatment.

The system and method described in UK patent no. GB2504097 covers the use of an apparatus comprising alternating beds of adsorbent material, which alternately act as the anode and the cathode. A flow of contaminated water passes continuously through both the anodic and cathodic beds. In the cathodic beds, the organic contaminants are adsorbed and not oxidised, but in the anodic bed, the organic contaminants are adsorbed and are additionally oxidised. When the current reverses, the anodic bed becomes the cathodic bed, and the cathodic bed becomes the anodic bed. Therefore, organic contaminants which were in the previously cathodic bed are now under oxidising conditions and are oxidised. The adsorbent surface of the previously anodic bed has been electrochemically regenerated and is therefore able to adsorb further organic contaminants from the liquid to be treated. The apparatus of the prior art is used to treat contaminated water in a batchwise manner, although continuous operation is known.

The system and method described in GB2504097 allows the use of a greater mass of adsorbent as there is adsorbent in both the anodic and cathodic compartments of the apparatus. In addition, the particulate adsorbent material has a greater surface area than a planar electrode so the current density may be lower, giving a reduced cell voltage. However, this system and method can lead to rapid organic breakthrough in the cathode compartment if the liquid is fed continuously though the system rather than in batches, but the adsorbent material in the cathodic compartment is not being electrochemically regenerated. In addition, certain organics do not easily adsorb to the adsorbent material and so the bed of adsorbent material may become saturated quickly and the organics may simply pass straight through the bed. Organic breakthrough is where the organic contaminants in the liquid to be treated are not adsorbed by the adsorbent material as they pass through the bed and the liquid exiting the apparatus retains high levels of organic contaminants. This usually occurs when the surface of the adsorbent materials is saturated and is consequently unable to adsorb further contaminants. Therefore, whilst there would be an initial reduction in the amount of organic contaminants in the liquid exiting the cathodic bed when the liquid to be treated is passed through a bed of adsorbent material which is not saturated, the adsorbent would quickly become saturated and therefore no further contaminants would be removed from the liquid and the level of contaminants exiting the bed would be the same as or substantially the same as the level of contaminants in the liquid before it is passed through the bed. In addition, as the bed is charged, a capacitance is built up in the bed. The capacitance is proportional to the surface area of the adsorbent. The high surface area of the adsorbent particles results in the system having a high capacitance, which may lead to a loss of performance when the current is reversed. In addition, repeated reversal of the direction of current flow can degrade the electrodes. During the further development of the systems described in UK patent no. GB2470042B and International patent application WO2010/149982 it became apparent that their performance in certain circumstances may be enhanced by the use of an external chemical dosing tank to maintain a low pH within the treatment zone for optimal performance. While performance advantages can be obtained by using an external means to maintain a low pH it would be desirable to obviate the need to provide the dosing tank since this adds to the cost and complexity of the overall decontamination process.

In prior art systems, such as those described in UK patent no. GB2470042B and International patent application WO2010/149982, the cathode is typically provided in an isolated cathode compartment fed with an electrolyte to ensure a high conductivity and therefore a low voltage between the electric current feeders. The electrode assembly consists of a micro-porous membrane, a cathode and chemical dosing system built into one inseparable, sealed "unit" to prevent catholyte leakage or the migration of adsorbent material from the anode compartment through to the cathode compartment. By way of example, one electrode assembly of size 500 mm x 500 mm may weigh approximately six kilograms and there can be a number of electrode assemblies in any one unit. If there is a fault with an individual part of the assembly, the entire assembly must be removed from the treatment tank and replaced. To maintain high conductivity in the cathode compartment, a membrane defining micro-pores maintains a high concentration of ionic components in the cathode compartment. The small diameter of the micro-pores prevents the rapid diffusion of ionic components from the solution in the cathode compartment into the solution in the anode compartment. However, suitable micro-porous materials can be unstable in alkaline conditions, which can add additional complexity to the overall treatment process. Furthermore the micro-porous material typically cannot prevent the osmosis of water from the anode compartment into the cathode compartment, which dilutes the electrolyte solution in the cathode compartment and necessitates the addition of further electrolyte throughout operation of the system. There is also the possibility of hydrogen accumulating in the electrode assembly due to the catholyte compartment being isolated. Conveniently, the chemical dosing system may be used to transport away any hydrogen that is produced, however, as mentioned above it would be desirable to obviate the need for the dosing system to reduce the cost and complexity of the system. An object of the present invention is to obviate or mitigate one or more of the problems currently associated with existing apparatus and methods for treating contaminated liquids.

According to a first aspect of the present invention, there is provided apparatus for the treatment of an aqueous organic waste liquid to provide a treated liquid containing less organic matter, the apparatus comprising:

a treatment reservoir defining first and second zones separated by a porous separator,

carbon-based adsorbent material capable of electrochemical regeneration provided in said first and second zones, the adsorbent material in each zone being coupled to a source of electrical power for providing a potential difference between the adsorbent material in each zone such that the adsorbent material in the first zone acts as an anode and the adsorbent material in the second zone acts as a cathode;

wherein the total surface area of the adsorbent material in the first zone is different to the total surface area of the adsorbent material in the second zone.

According to a second aspect of the present invention, there is provided a method for the treatment of an aqueous organic waste liquid to provide a treated liquid containing less organic matter, the method comprising:

passing the aqueous organic waste liquid into first and second zones of a treatment reservoir, the first and second zones being separated by a porous separator, each zone containing carbon-based adsorbent material capable of electrochemical regeneration, the total surface area of the adsorbent material contained in the first zone being different to the total surface area of the adsorbent material contained in the second zone,

adsorbing at least a portion of the organic matter onto the adsorbent material, operating first and second electric current feeders operably connected to the first and second zones respectively to pass an electric current through the carbon-based adsorbent material within each zone to regenerate the carbon-based adsorbent material in the anodic zone.

It will be appreciated that the apparatus and method of the first and second aspects of the present invention retain the advantages of having the conducting adsorbent material in the anodic and cathodic compartments of a cell, but avoid the need to reverse the current. By avoiding the need to reverse the flow of current, the inefficiencies in overcoming the capacitance effect are eliminated. In the systems of the prior art, since there is no difference in size of the cathodic and anodic beds, and since electrochemical oxidation of adsorbed pollutants takes place in the anodic bed, only the contaminated liquid which passes through the anodic bed is treated. Consequently, only around half of the liquid passing through a system having equal beds is treated. In order for more than half of the liquid to be treated, it is necessary to either reverse the current regularly or recycle the liquid back into the system after the first pass. With the present invention, it is possible to treat a greater proportion of the contaminated liquid without the need to recycle the liquid or reverse the current flow.

The voltage drop on the cathodic side is greater than on the anodic side so even with having a high surface area adsorbent acting as the cathode, there is a greater voltage drop on the cathode side. The total surface area of the adsorbent material may be reduced by any suitable means, including reducing the width or depth of the bed of adsorbent material. Thus, making the zone which acts as making the cathode narrower has the additional advantage of reducing the voltage drop on the cathode side. Another advantage of having a smaller cathodic zone is that the same number of hydroxide ions is formed as would be formed in a larger cathodic zone. However, in a smaller cathodic zone, the concentration of the hydroxide ions is greater than would be the case in a larger cathodic zone. Consequently, the conductivity of the liquid will be higher and less power is required to pass a current through the system. Further, a reduced cathode bed size reduces the flow of liquid to be treated through the cathodic bed and increases the proportion of liquid to be treated passing through the anodic bed. As such, a greater proportion of the liquid to be treated passing through the first and second zones will be subjected to anodic oxidation.

It may be desirable for the surface area of the adsorbent material in the cathodic zone to be greater than the surface area of the adsorbent material in the anodic zone in cases where reduction, rather than oxidation, of a contaminant is required. For example, the contaminated liquid may contain bromate ions and it is desirable to reduce the bromate ions to bromine.

In one embodiment of the first aspect of the present invention, the total surface area of the adsorbent material in the first zone is greater than the total surface area of the adsorbent material in the second zone. In an alternative embodiment, the total surface area of the adsorbent material in the second zone is greater than the total surface area of the adsorbent material in the first zone.

In the embodiment in which the total surface area of the cathodic adsorbent material is lower than the total surface area of the anodic adsorbent material, the total surface area of the adsorbent material in the anodic zone may be more than around 51 % of the total surface area of the adsorbent material in the cathodic and anodic zones combined and may be around 60% of the total surface area of the adsorbent material in the cathodic and anodic zones combined. The total surface area of the adsorbent material in the anodic zone may be around 70, 80, 90, or 95% of the total surface area of the adsorbent material in the cathodic and anodic zones combined. The surface area of the adsorbent material may be measured by any suitable technique, such as using the BET technique.

In the embodiment in which the total surface area of the adsorbent material in the anodic zone is lower than the total surface area of the adsorbent material in the cathodic zone, the total surface area of the adsorbent material in the cathodic zone may be more than around 51 % of the total surface area of the adsorbent material in the cathodic and anodic zones combined and may be around 60% of the total surface area of the adsorbent material in the cathodic and anodic zones combined. The total surface area of the adsorbent material in the cathodic zone may be around 70, 80, 90, or 95% of the total surface area of the adsorbent material in the cathodic and anodic zones combined. The surface area of the adsorbent material may be measured by any suitable technique, such as using the BET technique.

The adsorbent material in the first and second zones may be the same or different. However, it is preferred that the same adsorbent material is used in each zone in order to make filling of the apparatus with adsorbent material more convenient.

The total surface area of the adsorbent in the first and second zones may also be altered by utilising different adsorbent materials in the first and second zones. In this way, although the volume of the beds of adsorbent material in the first and second zones may be the same, if the beds comprise different adsorbent materials, the total surface area of the adsorbent materials in each zone may be different. Where the same adsorbent material is used in the first and second zones, it will be necessary for the zones to be of different sizes to provide the required difference in the surface area of the beds of the adsorbent material in the first and second zones.

Carbon-based adsorbent materials suitable for use in the methods and apparatus of the present invention are solid materials capable of convenient separation from the liquid phase and electrochemical regeneration. Preferred adsorbent materials comprise adsorbent materials capable of electrochemical regeneration, such as graphite, unexpanded graphite intercalation compounds (UGICs) and/or activated carbon, preferably in powder, granular, or flake form. Typical individual UGIC particles suitable for use in the present invention have electrical conductivities in excess of 10,000 Ω^"1 cm^"1. It will be appreciated however that in a bed of particles of the adsorbent material the electrical conductivity of the bed will be significantly lower as there will be resistance at the particle/particle boundary. Hence it is desirable to use as large a particle as possible to keep the resistance as low as possible. In addition the larger particles will settle faster allowing a higher flow rate to be achieved. However, increasing the particle size will result in a reduction in the available surface area, so a balance is required over high settlement rates and low cell voltages against the reduction in adsorptive capacity from a reduction in surface area. It will be appreciated however that a large number of different UGIC materials have been manufactured and that different materials, having different adsorptive properties, can be selected to suit a particular application of the method of the present invention. The adsorbent material may consist only of UGICs, or a mixture of such graphite with one or more other adsorbent materials. Individual particles of the adsorbent material can themselves comprise a mixture or composite of more than one adsorbent material. The adsorbent material may comprise a composite material of two or more carbonaceous materials. The adsorbent beds may comprise a mixture of two or more adsorbent materials. The kinetics of adsorption should be fast because the adsorbent material has no internal surface area and therefore the kinetics are not limited by diffusion of the organic contaminant to the internal surface. The adsorbent material may be NYEX™, which is sold by Arvia Technology Limited, UK. The apparatus and methods according to any aspect of the present invention may comprise any of the adsorbent materials according to the application entitled "Adsorbents for Treating Contaminated Liquids" filed on the same date as the present application by Arvia Technology Limited, the content of which is hereby incorporated by reference in its entirety.

The capability of materials to undergo electrochemical regeneration will depend upon their electrical conductivity, surface chemistry, electrochemical activity, morphology, electrochemical corrosion characteristics, and the complex interaction of these factors. A degree of electrical conductivity is necessary for electrochemical regeneration and a high electrical conductivity can be advantageous. Additionally, the kinetics of the electrochemical oxidation of the adsorbate must be fast. The kinetics depend upon the electrochemical activity of the adsorbent surface for the oxidation reactions that occur and also on the pH of the liquid phase. Electrochemical regeneration will generate corrosive conditions at the adsorbent surface. The electrochemical corrosion rate of the adsorbent material under regeneration conditions should be low so that the adsorption performance does not deteriorate during repeated cycles of adsorption and regeneration. Moreover, some materials can passivate upon attempted electrochemical regeneration, often due to the formation of a surface layer of non-conducting material. This may occur, for example, as a result of the polymerisation of the contaminant, for example phenol, on the surface of the adsorbent. Additionally, electrochemical destruction of the organic components on the adsorbent material will generate reaction products which must be transported away from the surface of the adsorbent material. The structure of the adsorbent material being regenerated can influence the rate of transport of the products away from the surface of the adsorbent material, and it will be appreciated that it is desirable to use adsorbent materials that facilitate this transport process. This will depend upon both the surface structure and chemistry of the adsorbent material.

It will be appreciated that preferred adsorbent materials for the present invention will desirably have an ability to adsorb organic compounds. The ability of the material to absorb is not essential, and in fact may be detrimental. The process of adsorption works by a molecular interaction between the organic component and the surface of the adsorbent. By contrast, the process of absorption involves the collection and at least temporary retention of an organic component within the pores of a material. By way of example, expanded graphite is known to be a good absorber of a range of contaminants (e.g. up to 86 grams of oil can be 'taken-up' per gram of compound). UGICs have effectively no absorption capacity. They can adsorb, but the adsorption capacity is very low as the surface area is low (e.g. up to 7 milligrams of oil can be 'taken-up' per gram of compound per adsorption cycle). These figures demonstrate a difference of four orders of magnitude between the take-up capacity of expanded graphite and that of UGICs. The selection of UGICs for use in the present invention arises from carefully balancing its high regeneratability against its relatively low take-up capacity.

Another advantage of the system of the present invention over the systems described in the prior art is that a variety of different materials can be used for the porous separator which separates the first and second zones. In the systems described in UK patent no. GB 2470042 and International patent application no. WO2010/149982, the solution in the cathode compartment has a high conductivity, whereas the solution in the anode compartment does not need to be conductive. In order to maintain high conductivity in the cathode compartment, a porous membrane material containing micro-pores maintains a high concentration of ionic components in the cathode compartment. The necessarily small diameter of the micro-pores prevents the rapid diffusion of ionic components from the solution in the cathode compartment into the solution in the anode compartment. Preferred materials containing micro-pores can be unstable in alkaline conditions, adding to the complexity of the treatment process. Furthermore the micro-porous material typically used cannot prevent the osmosis of water from the anode compartment into the cathode compartment, which results in dilution and an increase in the volume of the solution in the cathode compartment. The solution in the cathode compartment becomes a secondary waste upon completion of the treatment, so an increase in volume of said solution is not desirable. In the first and second aspects of the present invention, since both treatment zones contain adsorbent material, and a quantity of aqueous organic waste for treatment is distributed asymmetrically between the two treatment zones, there are no issues associated with the mixing of the liquid in the zone that behaves effectively as a "cathode compartment" and the liquid in the other zone which behaves effectively as an "anode compartment". Consequently, a range of different separator materials can be used in the apparatus and method of the first and second aspects of the present invention enabling more stable materials with a larger pore diameter to be used. The benefit of using a material with a larger pore diameter is that it offers a lower electrical resistance and therefore a lower voltage across the beds of adsorbent material. In addition, such materials are less susceptible to different pH conditions. The porous separator may be of any suitable construction and material. The porous separator is configured to prevent carbon-based adsorbent material from passing between the first and second zones, but to permit water and/or ionic species to pass between the first and second zones. The separator may be any material which prevents the carbon-based adsorbent material from passing between zones and from coming into direct contact with adsorbent material in another zone. If the adsorbent materials in neighbouring zones were to come into direct contact, this would result in the current being able to transfer between zones without entering the aqueous liquid, which would result in no or very little electrochemical oxidation of adsorbed contaminants. Materials such as paper or cotton wool may be used for the separator, although these are generally not preferred since they degrade rapidly.

Preferably, the separator is non-conducting. The separator is preferably non-conducting since this forces electrons out of the conductive adsorbent material and into the aqueous liquid. The ions pass through the pores in the porous separator and then re-enter the conductive adsorbent material on the other side of the porous separator. The current flows electronically through the adsorbent material and ionically through the separator. The majority of the electrochemical destruction of adsorbed contaminants takes place in the anodic region near to the separator. If the separator is conductive, the electric current could pass directly through the separator without entering the aqueous liquid and this would result in no or very little electrochemical oxidation of adsorbed contaminants. By having a nonconducting separator, the beds of conducting adsorbent materials in the first and second zones act essentially as a bipolar electrode. As such, it is possible to eliminate the need for heavy and expensive traditional bipolar electrodes, which are conventionally made from metal sheets, and instead allow the bed of conductive adsorbent material to act as the bipolar electrode. Therefore, another advantage of the methods and apparatus of the present invention is that having beds of adsorbent materials either side of the porous separator eliminates the need to have intermediate electrodes.

By having a separator which is porous, this allows ions to pass from one zone to another. Preferably, the separator allows the passage of water and ions through the pores in the separator. The separator may be permeable. The porous separator may be semi- permeable. In embodiments in which the porous separator is semi-permeable or selectively- permeable, this may allow ions to pass through the separator, but inhibit or restrict the passage of hydroxide ions through the separator. An accumulation of hydroxide ions in the cathodic zone increases the conductivity of the liquid in the cathodic zone and thereby reduces the power requirements of the system. Where the separator is permeable, this may allow the passage of small molecules, such as water, but may stop the passage of larger molecules and particles, such as the adsorbent material.

Preferably, the porous separator is made of a material which retains its integrity in aqueous environments. Preferably, the separator is able to withstand acidic and/or alkaline conditions. Such materials include ceramics, plastics, glasses, and the like. As such, sintered ceramic or glass may be used as the porous separator. The separator may comprise Daramic™ panels.

The source of electrical power may be first and second current feeders operably connected to the first and second zones. The first and second current feeders may be operated to apply any suitable electric current density to the carbon-based adsorbent material in the first and second zones to effect the desired level of oxidation of adsorbed organic matter. An electric current density of 0.001 to 30 imAcm^"2 may be employed, more preferably an electric current density of around 0.5 to 10 imAcm^"2, and most preferably an electric current density of around 2.5 imAcm^"2 may be applied by the current feeders to the carbon-based adsorbent material in each zone.

The first and second current feeders may be operated to apply any suitable electric current to the carbon-based adsorbent material in the first and second zones to effect the desired level of oxidation of adsorbed organic matter. An electric current of 0.01 to 50 amps may be employed, in one embodiment an electric current of around 5 amps may be applied by the current feeders to the carbon-based adsorbent material in each zone. The skilled person would appreciate that current density is of most importance to the regeneration of the adsorbent material and would be able to adjust the current employed to take account of the size of the system. As such, a system with a very large bed of adsorbent material may employ a current significantly in excess of 50 amps in order to reach the desired current density.

In one embodiment of the present invention, the aqueous liquid to be treated is able to flow through the anodic zone and the cathodic zone. Thus, since there is little or no destruction of contaminants flowing through the cathodic zone, there will eventually be organic breakthrough in the cathodic zone when the adsorbent material in the cathodic zone is saturated and is unable to adsorb any further contaminants. However, this may be useful in cases where it is not necessary to completely eliminate a contaminant from the aqueous liquid, but merely to reduce it below a desired level. For example, it may be the case that there are clean water regulations which specify that the concentration of a certain contaminant must be below a certain level. Thus, it may be possible to reduce the level of contamination to the required concentration without having to reduce the concentration to zero. The pH of the liquid in the anodic zone will be acidic due to the generation of hydrogen ions and the pH of the liquid in the cathodic zone will be alkaline due to the generation of hydroxide ions. Thus, the liquids leaving the cathodic and anodic zones may be combined to neutralise the pH of the liquids.

Where the contaminated liquid flows through both zones, the porous separator is preferably permeable. Since the liquid to be treated is passed though the cathodic bed, any hydroxide ions generated also pass through the bed and the separator and thus do not accumulate in the cathodic bed. As such, it is not necessary to use a semi-permeable porous separator to cause the hydroxide ions to accumulate and thereby increase the conductivity of the liquid and consequently reduce the cell potential.

However, in certain cases, such as when the contaminant is a microorganism, it is preferable to pass all of the liquid to be treated through the anodic zone in order to destroy the microorganism. It is important to seek to destroy every microorganism as any microorganisms which remain in the liquid may subsequently reproduce and potentially cause the treated liquid to become contaminated again. As such, in another embodiment of the present invention, the liquid to be treated is not allowed to exit the cathodic bed directly. This may be achieved by sealing the base of the cathodic bed or by any other suitable means. As such, when a liquid to be treated is first passed into the system, the cathodic zone will fill with the liquid. However, the liquid will not flow out of the cathodic zone. Once the cathodic zone is full, the liquid to be treated will therefore only pass through the anodic zone where it will be treated. As such, all of the liquid which passes out of the system will have passed through the anodic zone. In this embodiment, the porous separator is preferably semi-permeable. The semi permeable membrane will restrict the flow of hydroxide ions generated in the cathodic zone and thus the conductivity of the liquid in the cathodic zone will increase, which leads to a decrease in cell potential and a reduced power requirement. Thus, before an equilibrium is established, the pH of the water leaving the anodic zone will drop due to the increase in concentration of hydrogen ions. However, after a period of time, the hydrogen and hydroxide ions will transfer through the semi-permeable separator resulting in the neutralisation of the hydrogen ions in the anodic zone. Thus, the pH of the liquid leaving the anodic zone will begin to increase. Thus, there is auto-correction of the pH of the treated liquid once an equilibrium state has been reached. Depending on the flow rate of the liquid to be treated, any hydrogen generated may bubble out of the system or be entrained in the liquid exiting the anodic bed. Any microorganisms in the liquid contained in the cathodic bed are unable to pass through the separator and are therefore unable to contaminate the liquid in the anodic bed.

The majority of the hydrogen ions are produced next to the separator and the distance into the bed of the hydrogen ions depends on the conductivity of the liquid being treated. As such, there is less oxidation near to the current feeders.

The apparatus of the first aspect of the present invention may be used in the method of the second aspect of the present application. According to a third aspect of the present invention, there is provided apparatus for the treatment of an aqueous organic waste liquid to provide a treated liquid containing less organic matter, the apparatus comprising:

wherein the flow rate of the aqueous organic waste liquid through the first zone is different to the flow rate of the aqueous organic waste liquid in the second zone. According to a fourth aspect of the present invention there is provided a method for the treatment of an aqueous organic waste liquid to provide a treated liquid containing less organic matter, the method comprising:

passing the aqueous organic waste liquid through first and second zones of a treatment reservoir, the first and second zones being separated by a porous separator, each zone containing carbon-based adsorbent material capable of electrochemical regeneration, adsorbing at least a portion of the organic matter onto the adsorbent material, operating first and second electric current feeders operably connected to the first and second zones respectively to pass an electric current through the carbon-based adsorbent material within each zone to regenerate the carbon-based adsorbent material in the anodic treatment zone, wherein the flow rate of the aqueous organic liquid through the first zone is different to the flow rate of the aqueous organic waste liquid in the second zone.

In one embodiment of the third and fourth aspects of the present invention, the flow rate of the aqueous organic waste liquid is higher in the first zone than in the second zone. In an alternative embodiment, the flow rate of the aqueous organic waste liquid is higher in the second zone than in the first zone.

A larger proportion of the total amount of liquid passed through the anodic adsorbent material and the cathodic adsorbent material combined is passed through the anodic adsorbent material than is passed through the cathodic adsorbent material. More than around 51 % of the total amount of liquid to be treated passed through the anodic and cathodic adsorbent materials may be passed through the anodic adsorbent material. More than around 60%, 70%, 80%, 90%, or 95% of the total amount of liquid to be treated passed through the anodic and cathodic adsorbent materials may be passed through the anodic adsorbent material.

For example, where 90% of the total amount of liquid to be treated passed through the anodic and cathodic adsorbent materials is passed through the anodic adsorbent material, this means that the remaining 10% will pass through the cathodic adsorbent material. Any liquid flow which does not pass through either the anodic or cathodic adsorbent beds is not considered. Therefore, where there are multiple zones, it is possible to have multiple adsorbent beds. The apparatus of the third aspect of the present invention may be used in the method of the fourth aspect of the present invention. The apparatus and method of the third and fourth aspects of the present invention are similar to those of the first and second aspects of the present invention. As such, the features described above as relating to the first and second aspects are equally applicable to the third and fourth aspects of the present invention. As such, any combination of features described in respect of the first and second aspects of the present invention are applicable to the third and fourth aspects of the present invention, and vice versa.

The first and third aspects of the present invention provide apparatus for the treatment of an aqueous organic waste and are eminently suitable for the treatment of such waste in a continuous process. The treatment reservoir may be in the form of a tank or a chamber. The first and second zones may be defined within the treatment reservoir so as to be provided at any desirable location with respect to the treatment reservoir and with respect to one another provided the porous separator defines an interface between the two zones. It will be appreciated that the treatment reservoir may define two or more zones with a porous separator defining an interface between neighbouring zones. The porous separator may be configured to prevent carbon-based adsorbent material from passing between the first and second zones but to permit water and/or ionic species to pass between the first and second zones. In a preferred embodiment, the treatment reservoir contains two parallel or side-by- side beds of the carbon-based adsorbent material capable of electrochemical regeneration. The first and second zones may be configured to allow passage of the liquid substantially upwardly through the zones. Alternatively, the first and second zones may be configured to allow passage of the liquid substantially downwardly through the zones.

The second and fourth aspects of the present invention provide methods for the treatment of aqueous organic waste. When the electric current is fed through the beds of adsorbent material the bed operatively connected to the positive electric current feeder may be considered to behave as an anode and the bed operatively connected to the negative electric current feeder may be considered to behave as a cathode. It is preferable to continuously apply the electric current to oxidise organic components adsorbed on to the adsorbent material from the aqueous organic waste and to thereby continuously regenerate the adsorbent material in the anodic compartment. During this process, aqueous hydrogen ions are produced in the bed behaving as an anode and aqueous hydroxide ions are produced in the bed behaving as the cathode. The generation of hydroxide ions at the cathode is beneficial as it can result in the generation of increased conductivity in the cathodic zone, leading to a reduction in cell potential and therefore operating cost. The separator may be permeable or semi-permeable. If a semi-permeable separator is used to restrict, but not prevent the flow of ions, the system will eventually reach equilibrium where the transfer of hydroxide ions neutralises the hydrogen ions produced in the anodic zone.

In some embodiments according to the methods of the present invention, the electric current feeders may be operated continuously. In other embodiments, the electric current feeders may be operated intermittently.

In systems of the prior art, the key feature is that adsorption and electrochemical destruction of adsorbed contaminants takes place simultaneously, which allows for continuous treatment. However, some contaminants require relatively high voltages to achieve oxidation. For example, metaldehyde requires a minimum cell potential of 3 volts to ensure that the oxidation potential at the adsorbent surface is high enough to achieve organic oxidation. The higher oxidation potential can be achieved by increasing the current density, but this would result in an increase in power through both increased current and voltage, which results in higher costs.

Where there are only low concentrations of organic contaminants requiring high oxidation potentials in the liquid to be treated, only a small charge, but high voltage, may be required to oxidise the contaminants. If the current is applied continuously, only a small percentage of the charge is used to oxidise the contaminants and the rest is wasted on side reactions. This results in low current efficiencies. In addition, the increased oxidation potential and the large number of excess electrons can result in oxidative damage to the adsorbent material itself. It has been surprisingly realised that it is possible to operate the process and apparatus of any aspect of the present invention in an alternative manner by making use of the adsorptive capacity of the adsorbent material. The liquid to be treated may be passed through the bed of adsorbent material continuously resulting in the contaminants in the liquid being continuously adsorbed and concentrated on the surface of the adsorbent material. Due to the adsorptive capacity of the adsorbent material, the liquid may be passed through the bed of adsorbent material for some time before organic breakthrough occurs. Before organic breakthrough occurs, the current may be turned on at a current density high enough to produce the voltage required for oxidation of the particular compounds to be treated, in particular the organic materials which are adsorbed onto the surface of the adsorbent material. When the current is being applied, oxidation of the contaminants takes place and thereby regenerates the surface of the adsorbent to allow further contaminants to be adsorbed. The period of applying the current may be less than the period required for adsorption. Since the current is only applied intermittently, although the same current density is required, it is required for a shorter period of time. As such, the energy requirements are lower overall and cost savings can be achieved. In addition, the damage to adsorbent material through side reactions may also be reduced.

Although the intermittent application of current to regenerate the beds of adsorbent material has particular application in respect of the present invention, the skilled person would recognise that methods and apparatus for treating contaminated liquids utilising adsorbent materials may also benefit from intermittent operation of the current feeders.

As such, the current feeders may be operated intermittently. Preferably, the current feeders are operated prior to organic breakthrough occurs.

The current feeders may be operated at a first voltage which is sufficiently high to result in oxidation of a first contaminant and intermittently operated at a second voltage which is higher than the first voltage in order to oxidise a second contaminant. As such, the current can be varied to intermittently oxidise organic contaminants in the liquid to be treated. The current may be completely turned off between periods when the current is increased to a level required to oxidise adsorbed contaminants, or it may be reduced to a lower level in order to maintain a degree of current passing through the adsorbent material.

The variation in current densities applied to the adsorbent materials may be advantageous in cases where there is more than one contaminant in the liquid, the contaminants may require different oxidation potentials to be oxidised. In the prior art, the current density would have been held at a level required to oxidise the contaminant with the highest oxidation potential. As such, the power requirement would be high and energy costs would also be high.

In view of the possibility of intermittently applying a current, it is possible to use a solar powered system to provide the required power. As such, the current feeders may be connected to a photovoltaic cell, commonly referred to as a solar panel. During the day, the solar panel is able to generate direct current which can be passed to the current feeders and used to effect electrochemical oxidation of adsorbed contaminants. The power generated by the solar panel will vary during the day and will peak when the sun is at its strongest. Thus, adsorbed contaminants may be treated during the day. Following treatment, the treated liquid may be taken off and replaced with untreated liquid. The contaminants in the untreated liquid may be allowed to adsorb to the adsorbent material overnight and then be destroyed the next day when solar power is available once more. In addition to increasing the current applied to the bed of adsorbent material in order to treat organic contaminants with a high oxidation potential, it has also been surprisingly realised that it is possible to boost the oxidation potential in a system by using a chemical additive. In particular, it has been surprisingly realised that the addition of hydrogen peroxide to the methods and apparatus of any aspect of the present invention can enhance the performance of the system.

When added to the apparatus of the present invention, the hydrogen peroxide is reduced at the cathode to form water and a hydroxyl radical. Although treatment generally occurs in the anodic bed, the addition of hydrogen peroxide results in the production of a strong oxidising agent in the cathodic bed. As such, oxidation can be achieved in both the anodic and cathodic beds. The oxidation potential of the hydroxyl radical produced is 2.8 V, which is greater than that of ozone (2.08 V), chlorine (1 .36 V) or hydrogen peroxide (1 .78 V).

As such, there is provided the use of hydrogen peroxide in the apparatus and methods of any aspect of the present invention. The concentration of hydrogen peroxide may be maintained by addition of further amounts of hydrogen peroxide to balance the rate at which the hydrogen peroxide is consumed.

It is desirable to maximise the amount of contaminated liquid which may be treated in a given time period. The known approach for increasing flow through electrochemical cells is to increase the number of cells. These cells are usually stacked together in series with an electrical connection at both ends. The electrons are then free to pass from the electrode at one end to anode electrode at the other end through a series of electrochemical cells. The electrochemical cells contain intermediate electrodes. The intermediate electrodes act as bipolar electrodes where one face of the electrode acts as the anode and the other face acts as the cathode. However, according to the first to fourth aspects of the present invention, the adsorbent material itself may act as the bipolar electrode.

The cathodic reduction reaction occurs in the region close to the porous separator resulting in the transfer of electrons from the adsorbent into the aqueous phase. There is then ionic transfer of charge through the separator, with positive ions passing towards the cathode and negative ions passing towards the anode. On the opposite side of the porous separator, there is an oxidation reaction that occurs where there are organic contaminants adsorbed onto the adsorbent material. This will result in oxidation and the transfer of electrons from the adsorbed organic contaminant to the conducting adsorbent material. The electrons then pass through the adsorbent material to the next porous separator where the process is repeated. As such, the apparatus of the present invention can be produced more cheaply than the apparatus of the prior art as the intermediate electrodes can be removed. Since the generation of hydrogen ions and hydroxide ions is in similar quantities, the pH of the system remains constant. Therefore, the need to continually dose chemicals into the system in order to maintain the pH within the system at a constant level is eliminated. In the apparatus of the prior art, solid bipolar electrodes were used to guarantee that the current passed out of the liquid and into the electrode, through the electrode and then back into the liquid to be treated. However, it was surprisingly realised that it was possible to remove the heavy and expensive bipolar electrodes, and rely on beds of conductive adsorbent materials located on either side of a porous separator. Thus according to a fifth aspect of the present invention, there is provided apparatus for the treatment of an organic waste liquid to provide a treated liquid containing less organic matter, the apparatus comprising a treatment reservoir defining first and second zones separated by a porous separator, carbon-based adsorbent material capable of electrochemical regeneration provided in said first and second zones, the adsorbent material in each zone being coupled to a source of electrical power for providing a potential difference between the adsorbent material in each zone such that the adsorbent in the first zone acts as an anode and the adsorbent material in the second zone acts as a cathode; wherein the first and second zones are only separated by the porous separator. According to a sixth aspect of the present invention, there is provided a method for the treatment of an aqueous organic waste liquid to provide a treated liquid containing less organic matter, the method comprising:

passing the aqueous organic waste liquid into first and second zones of a treatment reservoir, the first and second zones being separated only by a porous separator, each zone containing carbon-based adsorbent material capable of electrochemical regeneration,

adsorbing at least a portion of the organic matter onto the adsorbent material, operating first and second electric current feeders operably connected to the first and second zones respectively to pass an electric current through the carbon-based adsorbent material within each zone to regenerate the carbon-based adsorbent material in the anodic zone. In the fifth and sixth aspects of the present invention, the total surface area of the adsorbent material contained in the first zone may be the same as or may be different to the total surface area of the adsorbent material contained in the second zone. Where the total surface area of the adsorbent in the first zone is different to the total surface area of the adsorbent material in the second zone, the total surface area of the adsorbent in the first zone may be greater than the total surface area of the adsorbent in the second zone and vice versa.

As mentioned above, aqueous hydrogen ions are produced in the bed acting as an anode and aqueous hydroxide species are produced in the bed acting as the cathode. As such, the apparatus may be operated without an external chemical dosing tank because the approximately equal amounts of hydroxide ions and hydrogen ions being produced maintains a consistent pH within the treatment system. The elimination of a chemical dosing tank reduces the complexity of the system, eliminates the need for chemicals to be delivered to the site on which the equipment is installed, and minimises the secondary waste associated with the treatment process.

A further advantage of the apparatus and methods of each aspect of the present invention over the apparatus and methods described in UK patent no. GB 2470042 and International patent application no. WO2010/149982 is that they can operate at low power and therefore low operating cost, without the presence of an isolated catholyte compartment. Low power operation is a consequence of a low voltage between the electric current feeders. Voltage is inversely proportional to solution conductivity and in the systems described in the prior art the isolated catholyte system provides a high conductivity and therefore a low voltage between the electric current feeders. An implication of the elimination of the catholyte system in the present invention is a decrease in conductivity of the solution between the electric current feeders. However, as established in "Electrochemical regeneration of a carbon- based adsorbent loaded with crystal violet dye"; N W Brown, E P L Roberts, A A Garforth and R A W Dryfe; Electrachemica Acta 49 (2004) 3269-3281 , cell voltage is proportional to the electric current density, which is a measure of electric current per unit area of the electrode and is therefore inversely proportional to the surface area of the electrode. In the cathode compartment of the present invention the bed of adsorbent material effectively behaves as a cathode which significantly increases the effective surface area of the "cathode" as compared to the cathode used in prior art methods, thereby lowering the current density and therefore affording a lower voltage. Consequently the present invention facilitates low power operation without the need for a separate catholyte compartment. That being said, since a low voltage across the beds of adsorbent material is preferable it may still be desirable to add an electrolyte to the bed of adsorbent material behaving as the high surface area cathode. The present invention allows for operation without an electrolyte but do not negate the use of an electrolyte if desired to lower the applied voltage beyond that achievable using the apparatus and method of the present invention.

According to any aspect of the present invention, the electric current can be adjusted to take account of variations in the concentration of organic contaminants, the nature of the organic contaminants, the flow rate of the liquid to be treated through the apparatus as well as for any other suitable reason. For example, where there is a high concentration of contaminants, it may be necessary to increase the size of the current passing through the adsorbent materials and the liquid in order to break down the contaminants. As a further example, certain contaminants may be more difficult to oxidise and therefore a higher current may be used to destroy such contaminants and thereby regenerate the adsorbent material.

Removal of the treated liquid from the treatment reservoir may be effected in any appropriate way. For example, one or more pumps may be used to cause the treated liquid to flow out of the treatment reservoir for storage or any desirable further use. Alternatively or additionally, removal may be effected by control of valves or partitions in between the treatment reservoir and an adjacent vessel, such as a storage tank. Alternatively or additionally, one or pumps may be used to cause the liquid to be treated to flow into the treatment reservoir. The liquid to be treated may be passed through the apparatus under the force of gravity.

Preferably, the liquid to be treated is pumped through the first and second zones such that the liquid to be treated contacts the adsorbent material at a flow rate which is sufficiently high to pass the liquid to be treated through the bed of adsorbent material, but below the rate required to fluidise the bed of adsorbent material. It will be appreciated that if the liquid is passed through the bed of adsorbent material at a rate which is greater than the rate at which the adsorbent material settles, this will result in fluidisation of the bed. Otherwise, if the rate at which the liquid is passed through the bed of adsorbent material is lower than the rate at which the adsorbent material settles, the bed will not be fluidised.

The liquid to be treated may be passed through the beds of adsorbent material in an upflow manner or a downflow manner. When the liquid to be treated is passed in an upflow manner, the liquid to be treated enters at or near to the bottom of the bed and passes generally upwardly through the bed and exits the bed at or near to the top of the bed. In contrast, when the liquid to be treated is passed in a downflow manner, the liquid to be treated enters at or near to the top of the bed and passes generally downwardly through the bed and exits the bed at or near to the bottom of the bed. Of course, it is recognised that the liquid may not enter or exit the bed at the absolute top or bottom of the bed, as appropriate, but it is the general direction of flow in the bed which determines whether the flow is 'upflow' or 'downflow'.

The electric current feeders preferably extend across the full height and width of the adsorbent beds to maximise their proximity to adsorbent particles loaded with organic component in need of regeneration. The electric current feeders will typically be provided on opposite sides of the beds of adsorbent material provided in the first and second treatment zones. A plurality of electric current feeders may be disposed along each side. Alternatively, multiple electric current feeders may be installed horizontally to allow different electric currents to be applied at different heights across the adsorbent beds during operation. In use, a voltage can be applied between the electric current feeders, either continuously or intermittently, to pass electric current through the adsorbent material and regenerate it.

The adsorbent material may be regenerated by electrochemical regeneration. By electrochemical regeneration, this is the process by which the surface of an adsorbent material may be regenerated. Organic contaminants, such as microorganisms or organic compounds, entrained within the liquid to be treated are adsorbed onto the surface of the adsorbent material when the liquid comes into contact with the bed of adsorbent material. When an electric current is passed through the adsorbent material, this can destroy the adsorbed contaminant in a number of ways. For example, where a microorganism is adsorbed on the surface of the adsorbent, the current may pass directly through the microorganism resulting in direct destruction of the microorganism. In addition, the localised increase in hydrogen ions during the oxidation of adsorbed organic material and water may lower the pH and thereby damage, destroy, or disrupt the adsorbed microorganism. Further, in cases where chloride ions are present, an oxidised chloride species may be generated by the current and this species may directly chlorinate the adsorbed microorganism. Similarly, adsorbed organic molecules may also be broken down by the same processes, of direct electron transfer, hydroxyl radical oxidation or mediated/indirect oxidation. The adsorbed contaminant may be oxidised into carbonaceous gases and water. These will desorb from the surface of the adsorbent material and the surface of the adsorbent material will consequently be available once again to adsorb further contaminants. Thus, the passage of current through the adsorbent material allows for a cycle of adsorption, electrochemical destruction and desorption of the oxidised adsorbed contaminants, followed by further adsorption. Preferably, the current is passed through the zones unidirectionally. The benefit of this is that no energy is wasted overcoming the capacitive effect of the beds and allows a more simple control mechanism to be used.

In order to clean the apparatus, it is possible to reverse the direction of the current. This assists in removing any deposits which may have built up on the current feeders/electrodes, in particular the current feeder/electrodes in the cathodic zone. The invention will now be described by way of example and with reference to the accompanying drawings wherein:

Figure 1 is a schematic perspective view of the apparatus of the prior art comprising a plurality of alternating beds;

Figure 2 is a schematic representation of the intermediate electrodes within an electrochemical cell stack of the prior art;

Figure 3 is a schematic representation of the adsorbent bed in the apparatus according to the present invention acting as a bipolar electrode;

Figure 4 is a schematic representation of the adsorbent bed in the apparatus according to an embodiment of the first aspect of the present invention in which liquid is able to pass out of the cathodic bed;

Figure 5 is a schematic representation of the adsorbent bed in the apparatus according the an embodiment of the first aspect of the present invention in which liquid is not able to pass out of the cathodic bed; Figure 6 is a schematic representation of the adsorbent bed in the apparatus according to the third aspect of the present invention; and

Figure 7 is a graph comparing the removal of 2,3-dichlorophenol using apparatus of the prior art and apparatus according to the first aspect of the present invention.

Figure 1 illustrates the apparatus of the prior art in which a plurality of electric current feeders 3 are closely aligned in a tank 1 in a parallel arrangement. Application of a voltage across the outer current feeders 3 polarises the intermediate electric current feeders 3, so effectively a series of alternate positive and negative current feeders are established between the outermost positive current feeder 3 and negative current feeder 3. The use of bipolar current feeders 3 in this way facilitates one current to be generated a number of times with a proportional increase in voltage. This increases the voltage to obtain a larger current in the adsorbent material 2 in sections of the bed of adsorbent material 2 between the electric current feeders 3 than would be achieved by the simple application of a larger voltage across the combined width of all of the beds of adsorbent material 2. The distance between the electric current feeders 3 can be varied depending on the organic loads and flowrates, but these distances would be kept as low as possible to minimise cell voltages. Typically, distances of about 25 to about 100 mm can be used, which is sufficient to allow the cell voltage to be kept at an acceptable level without creating blockages of the adsorbent material 2 and to allow the oxidised organic components removed from the aqueous organic waste to escape in the form of bubbles.

Each of the beds of adsorbent material are equally sized and the liquid to be treated is evenly distributed between the beds. The adsorbent material in each bed is the same. As such, an equal proportion of the adsorbent material acts as a cathodic bed and as an anodic bed when the system is in use. Therefore, at any one time, only half of the adsorbent material is undergoing electrochemical regeneration as electrochemical oxidation takes place in the anodic bed. The direction of the current is changed in order to swap the polarity of each bed and thus allow the adsorbent material in each bed to be alternately regenerated.

Figure 2 is a schematic representation of an electrochemical cell stack of the prior art showing the intermediate electrodes. In prior art cells, there are intermediate electrodes 5 and associated semi-permeable membranes 4. The intermediate electrodes 5 are solid and can be very heavy. The intermediate electrodes 5 act as bipolar electrodes, where one face of the electrode acts as the anode and the other face acts as the cathode. Figure 3 is a schematic illustration (not to scale) of the adsorbent bed in the apparatus according to the present invention acting as a bipolar electrode. In contrast to the apparatus of the prior art, there are no separate bipolar electrodes in the apparatus of the present invention, but rather the conducting adsorbent material in the first and second treatment zones acts as a bipolar electrode itself. The porous separator 6 is positioned in order to provide separate zones containing carbon-based absorbent material. The porous separator 6 and the beds of carbon-based adsorbent material either side of the separator 6 allow the adsorbent material either side of the separator 6 to act as a bi-polar electrode. This is possible due to the smaller gap between one current feeder and the separator 6 to provide a cathodic bed which is smaller than those of the prior art. There is ionic transfer of charge through the separator with positive ions passing towards the cathode and negative ions passing towards the anode. On the opposite side of the separator, there is an oxidation reaction that will occur where the organic contaminants are adsorbed to the adsorbent. This will result in oxidation and the transfer of electrons from the organic contaminant to the conducting adsorbent material. Where there are multiple separators, the electrons will then pass through the adsorbent to the next separator where the process is repeated. This process is able to occur because the conductivity of the adsorbent is around four orders of magnitude greater than that of water.

Figure 4 is a schematic representation of the adsorbent beds in the apparatus according to an embodiment of the first aspect of the present invention in which liquid is able to pass out of the cathodic bed. In this embodiment, there are two zones 7, 8 of differing sizes. In this embodiment, zone 7 comprises the cathodic bed and zone 8 comprises the anodic bed, although it will be appreciated that in other embodiments, the polarity of the beds may be the reverse. The two zones 7, 8 are separated by a porous separator 6. The two zones 7, 8 contain carbon-based adsorbent material and the adsorbent material is coupled to a source of electrical power. In this embodiment, current feeders 9, 10 are used to transfer the electrical power to the adsorbent material, although any suitable means may be used. During operation, liquid to be treated is passed through the beds of adsorbent material in the first and second zones 7, 8. In this embodiment, the liquid to be treated is shown as entering the bed as flows 1 1 , 12. These flows may be provided separate from one another, but may be provided from the same parent flow.

As the liquid passes through the beds, contaminants are adsorbed onto the surface of the adsorbent material. The current feeders pass an electrical current through the beds of adsorbent material, which causes electrochemical destruction of the adsorbed contaminants. The destruction of the contaminants adsorbed to the adsorbent material results in regeneration of the surface of the adsorbent material and allows further contaminants to adsorb to the surface. The oxidation of adsorbed contaminants occurs in the anodic zone, so the adsorbent material in the cathodic zone ultimately becomes saturated and is unable to adsorb further contaminants from the liquid. The liquid in the cathodic zone is able to exit the zone 7 as flow 13, and may be combined with flow 14 from the anodic zone. This is appropriate in cases where the contaminant does not need to be entirely removed from the liquid, but merely reduced below a particular level. Of course, it is possible that the flow 13 is taken off and not mixed with flow 14. The flow 13 may be passed back through the apparatus if further treatment is required.

Figure 5 depicts an apparatus which is largely similar to that depicted in Figure 4 and the same reference numerals are used for corresponding components. In contrast to the embodiment of the invention depicted in Figure 4, in this embodiment, the first zone 7 is sealed 15 at one end such that liquid is unable to exit the first zone 7 without passing at least partially through the second zone 8. In this way, there is no flow of liquid out of the apparatus which has not been treated and only treated liquid is able to exit the apparatus. This embodiment is preferred when the level of contaminant must be reduced as far as possible, such as when the contaminant is a microorganism. In such an embodiment, the porous separator 6 is selected to minimise contaminant transfer through the separator 6.

Figure 6 depicts an apparatus according to the third aspect of the present invention. It is largely similar to that depicted in Figures 4 and 5 and the same reference numerals are used for corresponding components. However, in this embodiment, the sizes of the beds are substantially similar, but the total surface area of the adsorbent material in one zone is greater than the total surface area of the adsorbent material in the other zone. This may be achieved by the use of different adsorbent materials. The adsorbent material in the cathodic zone 7 will eventually become saturated and will be unable to adsorb further contaminants. However, since contaminants which are adsorbed to the adsorbent material in the anodic zone 8 are oxidised, it is possible for the adsorbent material to be regenerated and is able to adsorb further contaminants. It will be appreciated that Figures 3 to 6 also depict an apparatus according to the fifth aspect of the present invention. In particular, in each of Figures 3 to 6, the two beds of adsorbent material are only separated by a porous separator 6. This is in contrast with the prior art systems depicted in Figures 1 and 2, which include intermediate electrodes in addition to semi-permeable membranes. Since the apparatus according to the fifth aspect of the present invention, as well as the first and third aspects, comprises a conductive adsorbent material in each zone, it is possible to discard the intermediate electrodes and only separate the beds of adsorbent material using a porous, non-conductive separator 6. This is also applicable to apparatus in which the beds are not uneven and can be used to simplify prior art designs.

Comparative Example In order to demonstrate the improved performance of the first aspect of the present invention, a comparative test was conducted in which the removal of 2,3-dichlorophenol (DCP) by two different apparatuses was compared. In one apparatus, the separator was placed in the middle of the gap between the electrodes to form equally sized beds and in the other apparatus, the separator was placed closer to the anode such that the bed of adsorbent material in the anodic zone was nine time wider than in the cathodic zone in order to form an apparatus having unequal beds. The apparatus with equal beds was operated in reverse current mode, which is where the polarity of the electrodes is reversed from time to time such that the beds change back and forth from being anodic to cathodic and vice versa. The apparatus with unequal beds was operated with current flow in a single direction. The current density used in both the equal and the unequal beds was the same, 2.5 imA/cm².

A common effluent was pumped through the two equal and unequal beds, and the concentration of DCP was measured. The rate of removal of DCP by each apparatus per hour was then calculated. The experiment was then repeated using a different flow rate.

Figure 7 shows the results of these comparative examples. When the flow rate used was 1 .6 l/h, the system with unequal beds removed around double the amount of DCP compared to the system with equal beds. When the flow rate was increased to 5 l/h, the system with unequal beds removed just under double the amount of DCP compared to the system with unequal beds. All aspects of the experimental set up were the same, other than the relative sizes of the beds.

The apparatus and methods of the first to sixth aspects of the present invention provide improved performance over systems of the prior art even when the same charge densities and adsorbent materials are used. The apparatus of the present invention allows a simpler cell to be produced, but which have improved performance compared to prior art cells. It is possible to eliminate heavy and expensive intermediate electrodes, which reduces costs.

Claims

1 . Apparatus for the treatment of an aqueous organic waste liquid to provide a treated liquid containing less organic matter, the apparatus comprising:

carbon-based adsorbent material capable of electrochemical regeneration provided in said first and second zones, the adsorbent material in each zone being coupled to a source of electrical power for providing a potential difference between the adsorbent material in each zone such that the adsorbent material in a first zone acts as an anode and the adsorbent material in a second zone acts as a cathode;

2. Apparatus according to claim 1 , wherein the total surface area of the adsorbent material in the first zone is greater than the total surface area of the adsorbent material in the second zone.

3. Apparatus according to claim 1 , wherein the total surface area of the adsorbent material in the second zone is greater than the total surface area of the adsorbent material in the first zone.

4. Apparatus according to claim 2, wherein the total surface area of the adsorbent material in the first zone is a greater than around 51 % of the total surface area of the adsorbent material in the first and second zones combined.

5. Apparatus according to claim 4, wherein the total surface area of the adsorbent material in the first zone is a greater than around 60% of the total surface area of the adsorbent material in the first and second zones combined.

6. Apparatus according to claim 5, wherein the total surface area of the adsorbent material in the first zone is a greater than around 70%, 80%, or 90% of the total surface area of the adsorbent materials in the first and second zones combined.

7. Apparatus according to claim 6, wherein the total surface area of the adsorbent material in the first zone is a greater than around 95% of the total surface area of the adsorbent material in the first and second zones combined.

8. Apparatus according to claim 3, wherein the total surface area of the adsorbent material in the second zone is a greater than around 51 % of the total surface area of the adsorbent material in the first and second zones combined.

9. Apparatus according to claim 8, wherein the total surface area of the adsorbent material in the second zone is a greater than around 60% of the total surface area of the adsorbent material in the first and second zones combined.

10. Apparatus according to claim 9, wherein the total surface area of the adsorbent material in the second zone is a greater than around 70%, 80%, or 90% of the total surface area of the adsorbent materials in the first and second zones combined.

1 1 . Apparatus according to claim 10, wherein the total surface area of the adsorbent material in the second zone is a greater than around 95% of the total surface area of the adsorbent material in the first and second zones combined.

12. Apparatus according to any preceding claim, wherein the adsorbent material in the first and second zones is the same.

13. Apparatus according to any preceding claim, wherein the carbon-based adsorbent material is an unexpanded graphite intercalation compound, activated carbon, graphite, a mixture of carbonaceous materials, or a composite of carbonaceous materials..

14. Apparatus according to any preceding claim, wherein the carbon-based-adsorbent material is in powder, flake, extruded, or granular form.

15. Apparatus according to any preceding claim, wherein the porous separator is configured to prevent the carbon-based adsorbent material from passing between the first and second zones but to permit water and/or ionic species to pass between the first and second zones.

16. Apparatus according to any preceding claim, wherein the porous separator is nonconducting.

17. Apparatus according to any preceding claim, wherein the porous separator is semipermeable.

18. Apparatus according to any preceding claim, wherein the porous separator comprises ceramic, plastic, polymeric, polyvinylidene (di)fluoride, Daramic™' and/or glass, and is preferably a porous, non-conducting material

19. Apparatus according to Claim 18, wherein the porous separator is sintered.

20. Apparatus according to any preceding claim, wherein the first and second current feeders are operated to apply any suitable current density to the carbon-based adsorbent material in the first and second zones to effect oxidation of organic matter.

21 . Apparatus according to claim 20, wherein the electric current density is from around 0.001 to around 30 imAcm^"2 , preferably from around 0.5 to 10 imAcm^"2, and more preferably around 2.5 imAcm^"2.

22. Apparatus according to any preceding claim, wherein the current is from around 0.01 to around 50 amps, and preferably around 5 amps.

23. A method for the treatment of an aqueous organic waste liquid to provide a treated liquid containing less organic matter, the method comprising:

24. A method according to claim 23, wherein the total surface area of the carbon-based adsorbent material in the first zone is greater than the total surface area of the carbon-based adsorbent material in the second zone.

25. A method according to claim 23, wherein the total surface area of the carbon-based adsorbent material in the second zone is greater than the total surface area of the carbon-based adsorbent material in the first zone.

26. A method according to any of claims 23 to 25, wherein the first and second current feeders are operated to apply an electric current density of around 1 to 30 imAcm^"2 to the carbon-based adsorbent material in each zone.

27. A method according to claim 26, wherein the electric current density applied is from around 0.5 to around 10 imAcm^"2.

28. A method according to claim 27, wherein the electric current density applied is around 2.5 imAcm^"2.

29. A method according to any one of claims 23 or 28, wherein an electrolyte is provided in the treatment reservoir.

30. A method according to any one of claims 23 to 29, wherein the carbon-based adsorbent material is an unexpanded graphite intercalation compound, activated carbon, a graphite, a mixture of carbonaceous materials, and/or a composite of carbonaceous materials.

31 . A method according to any one of claims 23 to 30, wherein the carbon-based adsorbent material is in powder, flake, extruded, or granular form.

32. A method according to any one of claims 23 to 31 , wherein the aqueous organic waste water is admitted to the reservoir at a rate which is sufficiently high to pass the aqueous organic waste water through the bed of adsorbent material, but below the rate required to fluidise the bed of adsorbent material.

33. A method according to any one of claims 23 to 32, wherein the waste water is passed downwardly through the first and second zones

34. A method according to any one of claims 23 to 32, wherein wherein the waste water is passed upwardly through the first and second zones

35. Apparatus for the treatment of an aqueous organic waste liquid to provide a treated liquid containing less organic matter, the apparatus comprising:

carbon-based adsorbent material capable of electrochemical regeneration provided in said first and second zones, the adsorbent material in each zone being coupled to a source of electrical power for providing a potential difference between the adsorbent material in each zone such that the adsorbent material in the first zone acts as an anode and the adsorbent material in the second zone acts as a cathode; wherein the flow rate of the aqueous organic waste liquid through the first zone is different to the flow rate of the aqueous organic waste liquid in the second zone.

36. A method for the treatment of an aqueous organic waste liquid to provide a treated liquid containing less organic matter, the method comprising:

passing the aqueous organic waste liquid through first and second zones of a treatment reservoir, the first and second zones being separated by a porous separator, each zone containing carbon-based adsorbent material capable of electrochemical regeneration,

adsorbing at least a portion of the organic matter onto the adsorbent material, operating first and second electric current feeders operably connected to the first and second zones respectively to pass an electric current through the carbon-based adsorbent material within each zone to regenerate the carbon-based adsorbent material in the anodic treatment zone, wherein the flow rate of the aqueous organic liquid through the first zone is different to the flow rate of the aqueous organic waste liquid in the second zone.

37. Apparatus for the treatment of an organic waste liquid to provide a treated liquid containing less organic matter, the apparatus comprising a treatment reservoir defining first and second zones separated by a porous separator, carbon-based adsorbent material capable of electrochemical regeneration provided in said first and second zones, the adsorbent material in each zone being coupled to a source of electrical power for providing a potential difference between the adsorbent material in each zone such that the adsorbent in the first zone acts as an anode and the adsorbent material in the second zone acts as a cathode; wherein the first and second zones are only separated by the porous separator.

38. A method for the treatment of an aqueous organic waste liquid to provide a treated liquid containing less organic matter, the method comprising:

39. A method according to any one of Claims 23 to 34, wherein the current is passed unidirectionally.

40. A method according to any one of Claims 23 to 34, wherein the current is reversed in order to clean the apparatus.